1. Field of the Invention
The present invention relates to a sheet supplying apparatus for separating and supplying a sheet one by one from a sheet stack, and more particularly, it relates to a structure of a sheet containing portion removably mountable in a sheet feeder portion.
2. Related Background Art
Generally, in sheet supplying apparatuses used with copying machines, printers, facsimiles and the like, a number of sheets (such as transfer sheets, photosensitive sheets and the like) are stacked on a sheet receiving plate of a cassette or deck, and such sheet is separated and supplied one by one from the stacked sheets (sheet stack) by means of a sheet supply means such as sheet supply rollers and the like and is fed toward a next processing station. In this case, to prevent a so-called double-feed, i.e., the fact that two or more sheets are supplied at a time, the provision of separating pawls is already known. More particularly, separating pawls are arranged at a leading end of the sheet stack with respect to a sheet supplying direction, and, when an uppermost sheet is supplied, it rides over the separating pawls while forming a loop at a leading end portion of the uppermost sheet, whereby the uppermost sheet is separated from the other sheets, with the result that only one sheet is supplied.
FIG. 31 is a perspective view of a main portion of an exemplary sheet supplying apparatus having separating pawls. In FIG. 31, the reference numeral 100 denotes a sheet stacking support (intermediate plate) acting as a sheet receiving plate; 101 denotes springs for biasing the sheet stacking support 100 upwardly; P denotes a sheet stack comprised of sheets (cut sheets or papers) having the same size; 102 denotes sheet supply rollers; and 103 denotes a pair of left and right separating pawls disposed on and engaged by front left and right upper corners of the sheet stack P with respect to a sheet supplying direction. An upper surface of the front or leading end portion of the sheet stack P is urged against lower surfaces of the sheet supply rollers 102 with a predetermined pressure by lifting the sheet stacking support by means of the springs 101. Alternatively, the sheet supply rollers 102 may be lowered to urge against the upper surface of the sheet stack P in response to a respective sheet supply signal. Each separating pawl 103 is pivotally mounted on a pin 103a for movement in an up-and-down direction so that the pawl is rested on the corresponding front corner of the sheet stack P by its own weight.
When the sheet supply rollers 102 are rotated in the sheet supplying direction, an uppermost sheet P1 of the sheet stack P is subjected to a feeding force directing toward the sheet supplying direction by the friction force between it and the sheet supply rollers 102. Thus, the uppermost sheet P1 tries to advance in the sheet supplying direction; however, since the left and right front corners of the sheet are restrained by the separating pawls 103, the uppermost sheet cannot advance in the sheet supplying direction. As a result, as the sheet supply rollers 102 are rotated, a bent loop E is formed in the uppermost sheet P1 near the separating pawls 103 between the sheet supply rollers 102 and the separating pawls 103 in opposition to the resiliency of the sheet P1. As a result, when the bent loop E grows up to a certain extent, by a restoring force tending to return the bent loop E to the original state, the left and right front corners (retained by the separating pawls 103) of the uppermost sheet P1 naturally shift from lower surface sides to upper surface sides of the separating pawls 103, thus riding over the separating pawls 103. This is to say, by forming and growing the bent loop E in the uppermost sheet P1, the latter is released from the separating pawls 103, with the result that only the uppermost sheet is separated from the other sheets P.
However, in the above-mentioned sheet supplying apparatus, since the leading end of the sheet stack rested on the intermediate plate always biased upwardly by the springs is urged upwardly to be abutted against the separating pawls and is stabilized, when an operator tries to replenish new sheets, he must push the intermediate plate down in opposition to the biasing springs and then replenish the new sheets between the intermediate plate and the separating pawls without interfering with the latter. Thus, the operability for replenishing the new sheets was unsatisfied.
Further, recently, pursuant to the increase in the frequency in use of sheets due to the variety of information, a cassette having the greater sheet containing ability than those of the conventional cassettes (for example, 500 sheets containable, whereas the conventional cases being 250 sheets containable) has been incorporated into a sheet supplying apparatus, so that the trouble regarding the replenishment of sheets has been partially eliminated. However, when sheets other than those having the greater frequency in use are used, since such sheets must be loaded within a cassette a little and then the sheets having the greater frequency in use must be re-loaded within the cassette, further trouble occurs. Further, if the remaining sheets are not kept under the proper conditions, such sheets will be undulated, dog-eared and(or) curled to change the condition of a sheet surface, and, thus, when they are used later, it is feared that the sheet is often jammed.
Further, when the cassette is mounted within or dismounted from the copying machine and the like for replenishing the new sheets or for performing the jam treatment or for changing the sheets of particular size to those of different size, the operability of the cassette is worsened. In addition, it is impossible to maintain a sheet separating and supplying condition (for separating and supplying the sheet one by one toward the next processing station) constant due to the increase in the sheet stacking amount; thus, when special sheets such as thicker sheets, thin sheets or the like are used, since they apt to cause the poor sheet supplying and(or) the double-feed, available kinds of sheets must be limited or the operating conditions of the copying machine and the like must be limited.